I have two elements that are fairly unrelated, the .menu, and the .content_selection_button. The only thing that ties them together is that they are both inside <li> elements in the same <ul>, other than that they share nothing. Yet, for some reason when I change the font-size of a .content_selection_button it affects the vertical placement of the menu. I had a similar problem here. Why is font-size ruining my placement, and how can I stop it?

@Oriol Yep, you are right - it is baseline.
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JohanVdRMar 21 '14 at 17:19

@JohanVandenRym but what does the baseline have to do with the menu. I had a similar problem where search button was out of alignment with the search bar because it was too big, but here they are separate elements.
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EasilyBaffledMar 21 '14 at 20:46

You've main parent element's with height 150px with LI inside 25% height. so that comes around 37.5px. The height wont increase due to the increase in font size, but it will affect the calculated line height, the line-height will increase pushing the text below a central axis of the button.